Buckling of asphalt shingles

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Buckling of asphalt shingles

B u c k l i n g o f A s p h a l t S h i n g l e s

"

Y

P.

J. S e r e d a and 11,

F,

S l a d e T h i s r e p o r t h a s b e e n p r e p a r e d f o r i n f o r m a t i o n and r e c o r d p u r p o s e s and i s n o t t o b e c i t e d as a r e f e r e n c e i n any p u b l i c a t i o n , I n t e r n a l R e p o r t No, 1 1 0 of t h e C i v i s i o n o f B u i l d i n , g R e s e a r c h Ottawa October 1956

PREFACE

T h i s i s a f u r t h e r p r o g r e s s r e p o r t on t h e work b e i n g done by t h e D i v i s i o n o f B u i l d i n g R e s e a r c h a t t h e r e q u e s t of C e n t r a l Mortgage and Housing Corpora t i on and i n c o - o p e r a t i o n w i t h t h e F o r e s t P r o d u c t s L a b o r a t o r i e s of t h e Department of N o r t h e r n A f f a i r s and N a t i o n a l R e s o u r c e s , i n 4 c o n n e c t i o n w i t h t h e problem of a s p h a l t s h i n g l e s on wooden r o o f s o F i e l d o b s e r v a t i o n s a r e a l s o b e i n g made i n t o t h e performance o f a s p h a l t s h i n g l e s on r o o f s c o n s t r u c t e d w i t h d i f f e r e n t w i d t h s o f b o a r d s , t h e o r i g i n a l i n q u i r y h a v i n g a r i s e n because of q u e s t i o n s r e l a t i n g t o CMHC s t a n d a r d s r e g a r d i n g s u c h board w i d t h s . A _{p r e v i o u s r e p o r t on work i n t h i s p r o j e c t was} DBR R e p o r t No.

84,

"The E f f e ' c t of M o i s t u r e on A s p h a l t S h i n g l e s n . Other r e p o r t s w i l l be i s s u e d t o d e s c r i b e o t h e r pha'ses o f t h e work, Comments on t h e c o n t e n t s of t h e p r e s e n t r e p o r $ w i l l be welcomed.

Ottawa,

B U C K L I N G OF ASPHALT SHINGLES P o J, S e r e d a and H, F, S l a d e A l t h o u g h t h e b u c k l i n g of s h i n g l e s on wood r o o f d e c k s h a s b e e n o b s e r v e d and r e p o r t e d , l i t t l e h a s b e e n done t o e s t a b l i s h t h e f a c t o r s r e s p o n s i b l e f o r t h i s p r o b l e m and t o s u g y ~ e s t s o l u t i o n s . 'i'he as.[:hal t s h i n g l e i n d u s t r y h a s c o n t e n d e d t h a t t h e u s e of b o a r d s no w i d e r t h a n

6

i n c h e s would m i n i m i z e t h i s p r o b l e m . It was o f i m p o r t a n c e t o t h e lumber i n d u s t r y t o show t h a t t h e w i d t h o f b o a r d s was n o t t h e o n l y p e r t i n e n t f a c t o r . A s a r e s u l t t h e F o r e s t P r o d u c t s L a b o r a t o r i e s and t h e D i v i s i o n of B u i l d i n ? E e s e a r c h were a s k e d by a l l t h e p a r t i e s c o n c e r n e d t o i n v e s t i g a t e t h e r e l a t i o n s h i p b e t w e e n t h e b u c k l i n g o f s h i n g l e s a n d t h e w i d t h o f r o o f b o a r d s , I n a r e c e n t r e p o r t

i t

h a s b e e n shown t h a t a s p h a l t s h i n g l e s a r e c o t d i m e n s i o n a l l y s t a b l e when e x p o s e d t o c o n d i t i o n s o f w e t t i n g a n d d r y i n g , The d i m e n s i o n a l i n s t a b i l i t y o f wood c a u s e d b y c h a n g e s i n m o i s t u r e c o n t e n t i s w e l l known, From t h e e x i s t i n g i n f o r m a t i o n a b o u t s h i n g l e s and b o a r d s , i t was p o s s i b l e t o a n a l y s e t h e e x p e c t e d movements of an a s s e m b l y o f b o a r d s and s h i n g l e s u n d e r e x t r e m e c o n d i t i o n s . It was of i n t e r e s t t o d e m o n s t r a t e e x p e r i m e n t a l l y w h e t h e r t h e p r e d i c t e d movements i n t h e b o a r d s and t h e s h i n g l e s d i d o c c u r , The f o l l o w i n g e x p e r f - m e n t s were d e s i g n e d t o p r o v i d e t h i s i n f o r m a t i o n , E x p e r i m e n t a l P r o c e d u r e and Samples T h i s i n v e s t i g a t i o n was c o n c e r n e d w i t h + t a b 2 1 0 - l b , a s p h a l t s h i n g l e s o n l y , An a p p a r a t u s w a s d e s i g n e d t o measure t h e h e i s h t o f b u c k l e p r o d u c e d i n a d r y a s p h a l t s h i n g l e f o r v a r i o u s r e l a t i v e movements o f t h e s h i n g l e n a i l s a t 5 - i n c h

c e n t r e s as would o c c u r when t h e wood d e c k s w e l l s o r s h r i n k s w i t h c h a n g e s i n m o i s t u r e c o n t e n t , T h i s a p p a r a t u s c o n s i s t e d o f a n a s s e m b l y of f o u r rows o f s h i n g l e s w i t h 5 - i n c h e x p o s u r e on two n i e c e s o f a - i n c h plywood, I n t h e t e a t a s s e m b l y ( F i g , l ) t h e two plywood d e c k s c o u l d b e moved h o r i z o n t a l l y r e l a t i v e t o e a c h o t h e r . S h i n g l e s were n a i l e d on t h e plywood d e c k f i r s t , i n t h e manner f o l l o w e d i n p r a c t i c e , w i t h t h e s h i n g l e t a b s s t a e g e r e d ; t h e n a new a s s e m b l y w a s n a i l e d w i t h t h e t a b s v e r t i c a l l y a l i g n e d , A s t h e b r e a k b e t w e e n t h e two plywood d e c k s w a s l o c a t e d b e t w e e n t h e s e c o n d and t h i r d row o f n a i l s , r e l a t i v e movement of t h e s e two d e c k s p r o d u c e d a b u c k l e i n t h e s e c o n d row of s h i n g l e s . The h e i g h t of b u c k l e w a s measured i n t h e

s l o t b e t w e e n t h e t a b s , The measurement w a s made w i t h a d i a l gauge a d a p t e d f o r t h i s p u r p o s e ( F i g - 1 ) .

A s s e m b l i e s o f a s p h a l t s h i n g l e s on wood d e c k s s e r v e d as s a m p l e s , Lumber u.sed f o r t h e s e sample s c o n s i s t e d

of

1 - i n c h

p i n e b o a r d s , 6 _{s n d 12 i n c h e s wide, These were n a i l e d t o}

2- by !!-inch s o r u c e r a r t e r s on 1 6 - i n c h c e n t r e s , Two n a f l s were u s e d f'or t h e 6 - i n c h b o a r d s and t h r e e f o r t h e 1 2 - i n c h b o a r d s , F i v e rows of 3 - t a b 210-lb, a s p h a l t s h i n p l e s were n a i l e d on t h e s e p r e p a r e d wood d e c k s e x p o s i n g

5

i n c h e s of t h e s h i n e l e s t o t h e w e a t h e r , The s h i n p l e nail p o s i t i o n s were marked and

i n d i c a t o r s were p l a c e d a t t h e c o n t a c t between b o a r d s an(' r a f t e r s t o i n d - i c a t e t h e mc;varnent of tlzat p o i n t of t h e board r e l a t i v e t o t h e r a f t e r , The i n d i c a t o r s c o n s i s t e d of a n e e d l e t h e end of which was h e l d i n a t i n y h o l e p r o v i d e d by a s t u d d r i v e n I n t o

t h e b o a r d , The n e e d i e had a p i v o t p o i n t consist in;^ of a h o l e

4

i n c h from t h e board t h r o u g h which a nai.1 was d r i v e n i n t o t h e r a f t e r , The o t h e r end of t h e 4 - i n c h n e e d l e f n d f c a t e d t h e move- ment o f t h e b o a r d m u l t i p l i e d 1 2 t i m e s , Tho manner o f i n s t a l - l a t i o n i s shown i n p h o t o g r a p h s ('FIg,2), R e f e r e n c e p o i n t s c o n s i s t i n g of b r a s s round-head n a i l s h a v i n g a 1/61+-inch h o l e d r i l l e d i n t o t h e h e a d s were d r i v e n i n t q t h e b o a r d s a t 2-inch c b e n t r e s t o e n a b l e t h e measurement of d i m e n s i o n a l changes due t o w e t t i n g o r d r y i n g , A d i a l gauge was a d a p t e d t o s e r v e a s an e x t e n s o m e t e r ,

Two sample a s s e m b l i e s c o n s i s t i n g o f 6- and 1 2 - i n c n wide b o a r d s were made a f t e r t h e b o a r d s had been c o n d i t i o n e d i n a room c o n t r o l l e d a t 50 p e r c e n t r e l a t i v e h u m i d i t y , Il'wcr o t h e r a s s e m b l i e s c o n s i s t i n g of

6-

and 1 2 - i n c h wide b o a r d s werae made a f t e r t h e b o a r d s had been cl7rlditioned i n t h e humid room con- t r o l l e d a t 100 p e r c e n t r e l a t i v e h u m i d i t y , The c o n d i t i o n s of m o i s t u r e c o n t e n t 3f t h e b o a r d s and s h l n p l e s a r e g i v e n i n

Table 1,

Thb s a m p l e s were c y c l e d between c o n d i t i o n s i n one room c o n t r o l l e d a t 50%

RH

and

7 3 ' ~ ~

and a n o t h e r room c o n t r o l l e d a t 100% RH and 74O~', The samples were k e p t a t e a c h condition f o r about one month a n d e a c h sample was given t h r e e cornpiete c y c l e s o r seven chanpes of c o n d i t i o n s , 1"Ieasurements were made a t t h e b e g i n n i n g and t h e end of e a c h h a l f c y c l e , The m o i s t u r e c o n t e n t of samr?les o f t h e s h i n g l e s was d e t e r m i n e d

a f t e r t h e l a s t c y c l e , R e s u l t s and D i s c u s s i o n

The d a t a from t h e e x p e r i m e n t d e s i g n e d t o show t h e r e l a t i o n s h i p between t h e movement of s h i n g l e n a i l s and t h e c o r r e s p o n d i n g s i z e of b u c k l e a1.e p r e s e n t e d i n F i g 0 3 , These show a c o n s i d e r a b l e v a r i a t i o n between t h e f i r s t c y c l e and

s u b s e q u e n t c y c l e s , T h i s car1 be a c c o u n t e d f o r by t h e f a c t t h a t a f t e r t h e f i r s t c y c l e a p l a n e of weakness was d e v e l o p e d i n t h e s h i n g l e a l o n g t h e l i n e where t h e s h i n g l e s b e n t t h e most,,

TABLE

I

--

SUMMARY OF

DATA

ON C O T u n I T ' I J1.S 03' BOARDS AND YHIBGLES FOR T'EIE

D u r i n g s u b s e q u e n t c y c l e s t h e r e f o r e t h e s h i n g l e would bend s h a r p l y a l o n e t h i s c e n t r e l i n e and would show a h i g h e r b u c k l e f o r t h e s a m e - * r e l a t i v e movement of t h e n a i l s , Thf s e f f e c t was n o t o b s e r v e d i n t h e s a m p l e s u n d e r s t u d y when t h e s h i n g l e s b u c k l e d d u e t o w e t t i n % : o r d r y i n g , D a t a p r e s e n t e d i n F i g ,

3

were o b t a i n e d w i t h d r y s h i n g l e s s u b j e c t e d t o r a p i d ~ . e l a t i v e movement of t h e d e c k , T h e r e f o r e t h e s e d a t a s h o u l d n o t be : i p p l i e d d i r e c t l y t o p r e d i c t t h e b u c k l e h e i g h t c o r r e s p o n d i n g t o a g i v e n movement i n t h e d e c k when t h e movement i s c a u s e d b y w e t t i n g o r d r y i n g i n v o l v i n g a slow r a t e

of change and when t h e s h i n ~ l e s a r e a t o t h e r t h a n t h e d r y s t a t e , Only l a r g e movements c a u s e d a f a i r l y r e p r o d u c i b l e b u c k l e , T a b l e 1 p r e s e n t s t h e e x p e r i m e n t a l d a t a of t h e m o i s t u r e c o n t e n t c h a n g e s and d i m e n s i o n a l c h a n g e s of t h e b o a r d s and t h e s h i n g l e s i n t h e s a m p l e s d u r i n g f i r s t c y c l e of w e t t l n g and d r y i n g , I t s h o u l d b e n o t e d t h a t t h e r e was c o n s i d e r a b l e v a r i a t i o n i n d i m e n s i 7 n a l chsn g e s of b o a r d s , The f a c t t h a t t h e p a r t of t h e s h i n g l e n e x t t o t h e b o a r d s p i c k e d up more m o i s t u r e t h a n t h e p a r t e x p o s e d t o t h e air i s s i g n i f i c a n t , T h i s may j u s t f f y t h e u s e o f 1 5 - l b , a s p h a l t f e l t under t h e s h i n g l e s , F i g u r e

4

p r e s e n t s t h e d a t a f r o m t h e f i r s t e x p e r i m e n t d e m o n s t r a t i n g t h e s w e l l i n g o f a s p h a l t s h f n g l e s on w e t t i n g , I n t h i s e x p e r i m e n t t h e s h i n g l e s were n a i l e d t o a m e t a l b a s e s o t h a t no movement of s h i n g l e n a i l s was p o s s i b l e and t.hen t h e a s s e m b l y was l e f t i n a room c o n d i t i o n e d t o

PO0

p e r c e n t

r e l a t i v e h u m i d i t y f o r a month, The b u c k l i n g of t h e s h i n g l e s i s shown g r a p h i c a l l y and c o r r e s p o n d s r o u g h l y t o t h e s w e l l i n g of t h e s h i n g l e by 0 , 0 5 i n c h i n

5

i n c h e s o r t h e equf v a l e n t of 2 p e r c e n t change i n a b o a r d 2 , s i n c h e s wide,

The e x p e r i m e n t a l and computed d a t a g i v i n g t h e movementis o f t h e s h i n g l e n a i l s w i t h t h e wood d e c k a n d t h e c o r r e s p o n d i n g b u c k l i n g o r t e a r i n g o f s h i n g l e s a r e p r e s e n t e d i n g r a p h f c a l form i n F i g u r e s

5,

6 , 7 and

8,

F i g u r e s

5

t o

8

a r e d r a t ~ n t o show t o s c a l e t h e p o s i t i o n s o f t h e s h i n g l e s and t h e i r n a i l s d e s i g n a t e d ( a ) , ( b ) , ( e ) , I d ) , and ( e ) w i t h r e s p e c t t o t h e b o a r d s and t h e i r c e n t r e l i n e s d e s i g - n a t e d 1, 2,

3,

4,

and

5 ,

The p o s i t i o n s A, B, C, and

D

on t h e s h i n g l e s d e n o t e t h e l i n e s between t h e s h i n ~ l e n a i l p o s f t i o n s a l o n g which b u c k l i n g was measured and a r e r e p r e s e n t e d on t h e v e r t i c a l s c a l e a t t h e e x t r e m e l e f t a s t h e h e i g h t of t h e b u c k l e i n i n c h e s , The c h a n g e s i n t h e h e i g h t o f t h e b u c k l e d u r i n g r e p e a t e d c y c l e s a r e r e p r e s e n t e d by s u c c e s s i v e l i n e s d i s p l a c e d t o t h e r i g h t and numbered 1 t o

3.

A t t h e r i g h t of t h e d i a g r a m

a r e shown m u l t i p l e g r a p h s w h i c h r e p r e s e n t t h e movements o f t h e s h i n g l e n a i l p o s i t i o n s (a), ( b ) # ( c ) , ( d ) , a n d ( e ) w i t h r e s p e c t t o t h e i r i n i t l a 1 p o s i t i o n s cnd w i t h r e s p e c t t o e a c h o t h e r ,

Thus a t any c y c l e t h e v e r t i c a l rlovement o f t h e s h i n g l e a t A ,

w i l l b e d e t e r m i n e d by t h e d i r e c t i o n a n d amount o f movement o f n a i l p o s i t i o r : ~ ( a ) , and (b), w i t h r e s p e c t t o t h e i n i t i a l y o s i t i o n shown a s z e r o , S i m i l ~ r l y t h e b e h a v i o u r o f s h i n g l e s a t

B,

C, and

D,

c a n b e p r e d i c t e d f r o m t h e c o r r e s p o n d i n g movements o f t h e a p o r o p r i a t e two s h i n g l e n a i l p o s i t i o n s ( b ) ( c ) , , C c ) ( d S , and ( W e ) . I n g e n e r a a l t h o c h a n g e s o c c u r r i n g on t h s f i r s t h a l f c y c l e were l a r p e i n c o m p a r i s o n t o t h o s e i n s u b s e q u e n t c y c l e s , T h e s e c h a n g e s r e p r e s e n t e d i r r e v e r s i b l e s h i f t s o f p o s i t i o n due t o llneven y i e l d i n g of n a i l s o r c r a c k s d e v e l o p i n g i n t h e b o a r d s , The d i r e c t i o n o f movement d u r l n g t h e f i r s t h a l f c y c l e was v e r y i m p o r t a n t and o f t e n d e t e r m i n e d t h e f u t u r e b e h a v i o u r o f t h e s a m p l e , lgor e x a r r p l e , i f t h e movement d u r i n g t h e f i r s t h a l f c y c l e was one of s e p a r a t i o n o f t h e two rows of s h i n g l e n a i l s , t h i s c a u s e d t h e t e a r i n g o f t h e n a i l h o l e s i n t h e s h i n b ~ l e and on t h e r e v e r s e c y c l e t h e movement c o u l d t a k e p l a c e w i t h o u t a f f e c t i n g t h e s h i n p l e , I n r e a l i t y t h i s w a s n o t a l w a y s t h e c a s e p o s s i b l y b e c a u s e t h e n a i l h o l e s were n o t e n l a r g e d s u f f i c i e n t l y d u r i n g t h d f i r s t h a l f c y c l e , when s t r e t c h i n g o f t h e s h i n g l e t o o k p l a c e , t o a l l o w f r e e movement of t h e n a i l i n t h e n a i l h o l e on t h e r e v e r s e c y c l e a n d t h u s some b u c k l i n g was o b s e r v e d i n m o s t of s u c h c a s e s ,

The i n s t a n c e s where s m a l l movements i n t h e wood d e c k w e r e accompanied by a b u c k l e o f c o n s i d e r a b l e s i z e a r e f u r t h e r e v i d e n c e t h a t t h e d i m e n s i o n a l c h a n g e s i n t h e s h i n g l e i t s e l f c o n t r i b u t e d t o t h e b u c k l i n g ,

When c a l c u l a t i n g t h e p r e d i c t e d movements o f t h e s h i n g l e n a i l p o s i t i o n s i n t h e wood d e c k t h e a s s u m p t i o n was made t h a t a l l movements o f t h e b o a r d would o c c u r s y m m e t r i c a l l y a b o u t t h e c e n t r e l i n e o f t h e b o a r d , The e x t e n t o f t h e movement w a s b a s e d on t h e m e a s u r e d d i m e n s i o n a l c h a n g e s t h a t o c c u r r e d i n t h e b o a r d s d u r i n g t h e c y c l i n g , From t h e d a t a p r e s e n t e d I n F i g ,

5

i t i s e v i d e n t t h a t s h i n p l e n a i l p o s i t i o n s ( d ) a n d ( e ) d i d n o t move a s p r e d i c t e d b u t r a t h e r s h i f t e d p o s l t i o n r e s u l t i n g i n a l a r g e b u c k l e a t D where a b u c k l e o f t h e s i z e shown a t A and R s h o u l d

have o c c u r r e d , F o r t h e sRme r e a s o n n o b u c k l e o c c u r r e d a t C a l t h o u g h i t s h o u l d have b e e n t h e same as a t A and B,

E x a m i n a t i o n o f t h e model of t h e a s s e m b l y o f s h i n s l e s on 6 - i n c h w i d e b o a r d s shows t h a t t h e - r e l a t i v e movement b e t w e e n

s w e l l i n g o r s h r i n k i n g of o n e - i n c h w i d t h of b o a r d , In e v e r y s i x t h row o f s h i n p l e s , however, t h e r e l a t i v e movement w i l l c o r r e s p o n d t o t h e movement due t o t h e s w e l l i n g o r s h r i n k i n g of 5 - i n c h

w i d t h of b o a r d b e c a a s e two rows of s h . i n g l e n a i l s w i l l be l o c a t e d i n t h e same b o a r d ,

The r e s u l - t s from sample 1 3 a p r e s e n t e d i n E'ig,

7

ahow

t h e l a r g e movements o f s h i n g l e n a i l p o s i t i o n s w h i c h a r e p o s s i b l e when 1 2 - i n c h wide b o a r d s a r e b e i n e w e t t e d f r o m t h e d r y s t a t e ,

P o s i t i o n s ( a ) and ( b ) , a l s o ( c ) and ( d ) u n d e r g o a r e l a t i v e mgvernent c o r r e s p o n d i n g t o t h e c h a n g e i n d i m e n s i o n d u e t o

swelling of a 7 - i n c h wide b o a r d , T h i s amounted t o a b o u t 0 , 2 i ~ c h and p r o d u c e d a b u c k l e of a l m o s t

$

i n c h , The movements and t h e b u c k l i n p i n t h i s c a s e were a l s p r o x i m a t e l y a s predicted,

The l a r g e r e l a t i v e s e p a r a t i o n o f n a i l p o s i t i o n s ( b ) and ( c ) , a l s o ( d ) a n d ( e ) i n F i g , 7 c a u s e d b j s w e l l i n g o f 5 - i n c h w i d t h of b o a r d c a u s e d a t e a r i n g of t h e s h i n g l e n a i l h o l e s b y a b o u t

l / 8

i n c h ,

The r e s u l t s f r o m sample 13b a s shown i n F i g ,

8

i l l u s t r a t e t h a t t h e s h r i n k a g e o f b o a r d s t h a t are n a i l e d when w e t can c a u s e c r a c k s t o d e v e l o p w i t h t h e r e s u l t t h a t moverrents o f s h i n g l e n a i l p o s i t i o n s c a n b e v e r y d i f f e r e n t f r o m what t h e y a r e p r e d i c t e d t o b e . A _{good example i s t h e s h i n g l e n a i l p o s i t i o n s ( b ) and}

( c ) i n F i g ,

8

b ~ h e r e a l a r g e b u c k l e a t B s h o u l d h a v e o c c u r r e d , The b o a r d c r a c k e d a t a b o u t t h e m i d - p o s i t i o n c a u s i n g l i t t l e movement a t t h e s h i n g l e n a i l p o s i t i o n s , There s h o u l d n o t have b e e n b u c k l i n g of s h i n g l e s a t A and C a s i s shown, T h i s b u c k l i n g a t A _{and C c a n o n l y b e e x p l a i n e d b y c o n s i d e r i n g t h a t p a r t of}

i t i s due t o t h e s w e l l i n ? o f t h e s h i n q l e and p a r t due t o t h e g r i p p i n g of t h e n a i l i n t h e s h i n [ < l e a t t h e new e x t e n d e d p o s i t i o n c o r r e s p o n d i n g t o t h e f i r s t h a l f c y c l e . Summarv a n d C o n c l u s i o n s These e x p e r i m e n t s h a v e d e m o n s t r a t e d t h a t a s p h a l t s h i n g l e s w i l l b u c k l e a s a r e s u l t o f t h e r e l a t i v e movement due t o s w e l l i n g o r s h r i n k i n : ? o f t h e b o a r d s t o which t h e s h i n g l e s a r e n a i l e d and a l s o a s a r e s u l t o f s w e l l i n g o f t h e s h i n g l e i t s e l f when t h e m o i s t u r e c o n t e n t i s c h a n g e d , I t h a s b e e n shown t h a t t h e c h a n c e s o f l a r g e b u c k l e s b e i n g p r o d u c e d a r e g r e a t e r w i t h 1 2 - i n c h wide h o a r d s t h e n 1 . r T l - t ?

6 - i n c h wide b o a r d s , I t i s a l s o e v i d e n t when 1 2 - i n c h wide b o a r d s a r e u s e d and t h e f i r s t

$

c y c l e i n v o l v e s a d r y i n g of

t h e i n i t i a l l y w e t b o a r d s ( a c a s e most l i k e l y t o o c c u r i n p r a c t i c e ) t h a t t h e r e i s a good c h a n c e t h e b o a r d s w i l l c r a c k l o n g i t u d i n a l l y and w i l l n o t p r o d u c e t h e b u c k l i n g t h a t would b e e x p e c t e d ,

The r e s u l t s i n d i c a t e t h a t b o a r d s n a i l e d t o r a f t e r s w i t h two o r t h r e e n a i l s c a n n o t be e x p e c t e d t o s w e l l o r s h r i n k s y m m e t r i c a l l y a b o u t t h e i r c e n t r e l i n e s , The l o n g i t u d i n a l c r a c k i n g and uneven y i e l d i n g of n a i l s c o n t r i b u t e s t o t h i s , I n c o n c l u s i o n i t c a n be s a i d t h a t some d e g r e e of b u c k l i n g o f - s h i n g l e s i s t o be e x p e c t e d where t h e s h i n g l e s a r e n a i l e d

w i t h two rows of n a i l s a s l o n g a s b o t h t h e s h i n g l e and t h e wood d e c k a r e d i m e n s i o n a l l y u n s t a b l e w i t h c h m g e s i n m o i s t u r e a e o n t e n t ,

R e f e r e n c e s

(1) Ayukawa, Muand P . J . S e r e d a , The e f f e c t of m o i s t u r e on a s p h a l t s h i n g l e s , N a t i o n a l R e s e a r c h C o u n c i l of Canada, D i v i s i o n of B u i l d i n g R e s ~ a r c h , I n t e r n a l R e p o r t No,

84,

D%aP gauge used f o p m e a s w i n g the

b u c k l e height,

Apparatus used f o p % % n d f n g the relatlsnskip

between b u c k l e hefght and corresponding

c h a n g e in the 5-fnch span between two rows

of _{s h i n g l e 13~3118,}

FIGURE

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the i n d i c a t o r s , F I G r n E 2

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SHINGLE BUCKLE DURING 3 CYCLES MOVEMENT OF SHINGLE NAIL POSITIONS IN WOOD DECK DURING 3 CYCLES

FIGURE 5

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SHINGLE BUCKLE DURING 3 CYCLES MOVEMENT OF SHINGLE NAIL POSITIONS IN WOOD DECK DURING 3 C Y C L E S

FIGURE 6

BUCKLING OF ASPHALT SHINGLES

8

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FIGURE

7

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drying X - - - - X L I I I I I I I I I I I I I I I 0 4 8 12 16 2 0 2 4 2 8 INCHES

SHINGLE BUCKLE DURING 3 CYCLES MOVEMENT OF SHINGLE NAIL POSITIONS IN WOOD DECK DURING 3 CYCLES

FIGURE 8

BUCKLING OF

ASPHALT

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WOOD DECK. DRY SHINGLES APPLIED ON WET 12 INCH WIDE BOARDS.